As a method of bonding an electronic component such as a semiconductor device to a board, a soldering bonding method is known in the art. The soldering bonding method has many advantages. For example, an electronic component can be bonded within a short time, a thermal deterioration generated from a soldering temperature change can be reliably controlled, and a plurality of electronic components can be bonded through a single reflow process.
However, the soldering bonding method has some disadvantages. For example, it is difficult to bond a plurality of electrode terminals of the electronic components with a minute interval, and electric and thermal conductivities of the solder are lower than those of silver and the like.
Meanwhile, as a method of bonding an electronic component to a board, there is known a solid-state diffusion bonding method in which the bonding is performed through a heating or pressing process or by applying ultrasonic vibration (for example, refer to Japanese Unexamined Patent Application Publication No. 2010-118534).
The solid-state diffusion bonding method is a method of using an atom diffusion phenomenon generated between metals (electrodes) insoluble by heating or pressing under a certain condition. In general, the solid-state diffusion bonding is performed at a temperature of, for example, several hundred degrees centigrade, which is lower than a melting point of the solder. Therefore, it is possible to lower a bonding temperature, compared to the soldering bonding method.
As such a solid-state diffusion bonding method, for example, there is known a method of directly bonding the electrode of the board and the electrode terminal of the electronic component by applying a predetermined pressure and a predetermined temperature or a bonding method by coating a metallic impalpable powder paste between the electrode terminal of the electronic component and the electrode of the board and solidifying the metallic impalpable powder paste.
The solid-state diffusion bonding method is advantageous in that it is possible to obtain an excellent heat resistance and a high electric or thermal conductivity. Therefore, the solid-state diffusion bonding is employed in various technical fields requiring an excellent thermal or electric characteristic, such as connection of a next-generation power semiconductor such as SiC (silicon carbide) or GaN (gallium nitride) or a high-luminance light-emitting diode (LED) or bonding of a large-scale integration (LSI) circuit.
Meanwhile, the solid-state diffusion bonding has some disadvantages. For example, a high pressure and a longer time are necessary to generate a sufficient diffusion reaction compared to the soldering bonding method.
Typically, a plurality of electronic components are bonded to a board. However, in some cases, each electronic component may have a different height, when a plurality of electronic components is bonded. In such a solid-state diffusion bonding of the related art, each electronic component is interposed between individual heaters, and a predetermined temperature and a predetermined pressure are applied to each of the electronic components for a certain time.
However, in the method of applying a predetermined temperature and a predetermined pressure for a certain time while each electronic component is interposed between individual heaters, a heater for the heating and a motor for the pressing are necessary for each electronic component. Therefore, a manufacturing cost of an element bonding apparatus (bonder) increases, and more time is necessary to perform the diffusion reaction. Therefore, productivity decreases disadvantageously.
In addition to the height difference, evenness is also different between a plurality of electronic components bonded to a board. Therefore, in order to evenly press a plurality of electronic components to bond them to a board, a highly accurate control such as adjustment of evenness is necessary. This may also degrade productivity.
In recent years, as electronic devices are miniaturized, a demand for miniaturization of a board also increases, and a distance between electronic components bonded to a single board or a pitch between terminals of the electronic components tends to be shortened. However, a large space is necessary to arrange heaters for heating each electronic component and a motor for applying a pressure. Therefore, in the method of applying a predetermined temperature and a predetermined pressure for a certain time by interposing each electronic component between individual heaters, it is difficult to bond the electronic components when a distance between electronic components or a pitch between terminals of electronic components is small. This makes it difficult to miniaturize the board.
Meanwhile, as a method of bonding a plurality of electronic components having different heights to a board using the solid-state diffusion bonding of the related art, there is known a bonding method in which a plurality of electronic components are disposed in a liquid to apply a hydrostatic pressure of the liquid to a plurality of electronic components while the liquid is heated (refer to paragraphs [0044], [0046], and the like of Japanese Unexamined Patent Application Publication No. 2012-89740).